Overcharging customers

I am currently having problems with getting response from multichoice dstv for overcharging me.My problem started when I took a prizelock contract with them in September.When I talk to an agent she explained to me that since I was activated on the 25/09/19 I will only pay a prorata for 5 days that I have been using it.To my surprise multichoice debited my account with full amount of R549 instead of 5 days prorata. Since the I have been calling multichoice weekly triying to resolve my account problem without any help.Everytime when I contacted them they agent promiseto call me back after 48 hours and to date I have not recieved their call though they confirmed to me that their system have a problem and most prizelock customers were over billed.I am very disappointed by their service